No, due to the method of installation that Vista uses, you can not do a "Repair"
install of Vista. You can do an in-place upgrade, where you "upgrade" vista as
if you were upgrading XP, or possibly use the repair tools from booting from the
DVD, but there isn't a repair install function.
I installed Vista Beta 2 on one of my computers with a Vista Beta 2
installation and pointed to the partition where Vista already was, and
the installer put the 'old' Vista into a folder named 'Windows.old'.